(1) Field of the Invention
The invention relates to a track coater unit cup set, which is utilized in IC fabrication processes, especially in a spinning process; and more particularly to a modified track coater unit cup set in which the induced solvent spraying accuracy and the resulted cleanliness on the wafer in the involving process can be greatly improved by little reworking on the cup set profile.
(2) Description of the Prior Art
In the coating processes of a wafer in the semi-conductor industry, spin coating is the general application in adding a thin film or membrane on the wafer. Such a thin film can be a photoresist, etching agent, or the like to coat over the wafer surface. In the spin application of the art, the wafer is positioned upon a vacuum susceptor, and the chemical solvent to form the film is dropped from top of the wafer while it rotates with the susceptor driven by a rotation mechanism. During the spinning, at least a spray post located under the susceptor is used to provide cleaning solvent spray onto the rim of the wafer, so that the chemical residues over the rim can be washed out at the same time. By proving such a cleaning spray, possible inaccurate problems close to rim of the wafer can be reduced to a minimum.
In the conventional arrangement of a spin facility, it generally involves a track coater unit cup set to work with the cleaning solvent spray for reducing the possibility of the solvent contaminating the wafer or the spin facility
Referring now to FIG. 1, a track coater unit cup set and the related part of the rotation mechanism are shown exposedly. As shown, the track coater unit cup set 1 on top of the rotation mechanism 2 is a kit with three circular parts. The first part is a hollow concave base cup 11 capable of anchoring on the rotation mechanism 2, the second is a hollow convex inner cup 13 located on top of the base cup 11, and the third is a hollow convex outer cup 15 to envelope the inner cup 13 and to be placed on top of the base cup 11. In piling the track coater unit cup set I onto the rotation mechanism 2 for application, the base cup 11 is firstly fixed to the rotation mechanism 2. Secondly, the inner cup 13 with the maximum diameter less than that of the base cup 11 is placed on top of the base cup 11. Thirdly, engage a susceptor 21 with a shaft 23 over the inner cup 13, in which the shaft 23 is extended from the rotation mechanism 2 and through the hollow openings of the base cup 11 and the inner cup 13. The susceptor 21 is used to carry a wafer (not shown in 15FIG. 1) on top for undertaking a spin coating process. Finally, the outer cup 15 is used to go with the base cup 11 for forming an internal space in between to include the inner cup 13 and the susceptor 21 as well as the wafer thereinside.
Referring now to FIG. 2, a cross sectional view of the assembly of the track coater unit cup 1 and the rotation mechanism 2 is shown. As shown, the base cup 11 rides on the rotation mechanism 2 and has the central opening for top of the rotation mechanism 2 to penetrate. The base cup 11 further includes two concentric circular grooves: an inner circular groove 111 and an outer circular groove 113. An inner wall of the inner circular groove 111 is defined as an inner groove wall 115. On the other hand, the outer surface of the inner cup 13 is used as a flow-leading surface. As shown in FIG. 2, the inner cup 13 has an inner downward protruding ring 1311 for engaging with the inner groove wall 115 of the base cup 11 through a first step-shape engaging structure established along the meshing interface 1110 between the top edge of the inner groove wall 115 and the lower end of the protruding ring 1311. The outer lower end of the inner cup 13 is designed to suspend in the outer circular groove 113 of the base cup 11, so that the cleaning solvent can be led into the outer circular groove 113 through the outer surface of the inner cup 13, after the solvent hitting the rim of the wafer 3. The accumulated cleaning solvent is then led out through a hole (not shown in figures) on the bottom of the outer circular groove 113. The upper central opening of the inner cup 13 is defined as an upper opening 131, through which the driving shaft 23 of the rotation mechanism 2 can penetrate. At the upper end of the shaft 23, there locates the susceptor 21 for vacuuming the wafer 3 on top thereof. The area of the upper opening 131 is no more than either that of the top of the rotation mechanism 2 or that of the wafer 3. The outer cup 15 is used to enclose totally the outer circular groove 113 of the base cup 11. Generally, the lower end of the outer cup 15 engages with the top end of the outer wall of the outer circular groove 113 (also the outer wall of the base cup 11) through a second step-shape engaging structure 1113 formed in-between. The upper central opening of the outer cup 15 is defined as a top opening 151. The space formed between the outer cup 15 and the inner cup 13 is defined as a working space 350, in which the wafer 3 undergoes the coating process. The rim of the outer cup 15 to form the upper opening 151 further includes a ring of short inward tip 153 protruding into the working space 350. The purpose of the inward tip 153 is to substantially smooth out the airflow introduced into the working space 350 through the upper opening 151.
During a coating process, the susceptor 21 as well as the wafer 3 is rotated by the shaft 23 of rotation mechanism 2. Photoresist or other chemical for forming a thin film on the wafer 3 is added through the top opening 151. By the rotation induced centrifugal force, photoresist or other chemical can be spread to cover the whole wafer 3. In order to achieve smoothness and to avoid possible splash of the photoresist and other chemical, a ventilation system (not shown in figures) for vacuuming the working space 350 can be provided to the bottom of the base cup 11. To avoid the photoresist or other chemical to residue at the rim of the wafer 3 (which may induce particle contamination and the planarization problems on the wafer 3 thereafter), the rotation mechanism 2 usually includes a pair of spray posts 25 for providing cleaning solvent spray 251 onto the rim of the wafer 3. For the spray 251 to penetrate the upper opening 131 and arrive at the rim of the wafer 3, the inner cup 13 further has a pair of respective apertures 133 located along the inner rim thereof. The cleaning solvent spray 251 is provided by the spray posts 25, hits the rim of the wafer 3, and then drops between the inner cup 13 and the outer cup 15. The cleaning solvent together with the residue photoresist or other chemical then flow into the outer circular groove 113 of the base cup 11. Finally, the cleaning solvent together with the residue photoresist or other chemical are led out of the track coater unit cup set 1 from the bottom of the base cup 11.
In the aforesaid structure, the track coater unit cup set 1 generally has two disadvantages. One is the misalignment problem between the spray 251 and the aperture 133, and the other is the aggregation and solidification of the solvent at the comer close to and at the inward tip 153.
Regarding the misalignment between the spray 251 and the apertures 133, the problem results from the angular shifting between the base cup 11 and the engaged inner cup 13, due to the vibration caused the driving system of the rotation mechanism 2. Furthermore, the light weight on the inner cup 13 (usually made of plastic or non-metallic material), which contributes to less normal force on the meshing interface 1110 and thus less friction force thereon to prevent from the relative motion between the inner cup 13 and the base cup 11, makes worse the angular shifting problem. As a consequence of the angular shifting, the spray 251 injected from the spray post 25 cannot normally pass through the corresponding aperture 133, but hits the inner wall of the inner cup 13; so that insufficient solvent flow can be provided to clean the rim of the wafer 3 and the contamination problem on the rotation mechanism 2 may arise. In the literature, two measures have been provided to resolve the misalignment problem. One is to frequently caliber the angling between the base cup 11 and the inner cup 13, the other is to enlarge the aperture 133. However, the former measure will result in the decrease of the manufacturing effectiveness, and the later measure will inevitably increase the coming-back solvent amount through the enlarged aperture 133. None of them can really ease this disadvantage.
Regarding the aggregation problem close to and at the inward tip 153, the reason that causes the aggregation of the solvent is the unique geometrical profile in the neighborhood of the inward tip 153. By the analysis of the fluid dynamics, a certain amount of drifting micro liquid drops will be generated wile the spray 251 breaks through the air in the working space 3501 and after the spray 251 hits the rim of the wafer 3. Such drifting drops may be driven by the turbulence to circulate within the so-called stall-flow region 3501 formed close to the inward tip 153 and the inner wall of the outer cup 15. The micro drifting drops in the stall-flow region 3501 will eventually aggregate to form a bigger droplet and then drop into the outer circular groove 113 of the base cup 11. However, in another aspect, the micro drifting drops will aggregate on the inner wall of the inward tip 153, and will fall onto and contaminate the wafer 3 after a substantial amount of solvent accumulated on the inward tip 153. Otherwise, the solvent residue on the inward tip 153 will solidify and form a possible particle source to contaminate the following wafer 3 in the same process. To overcome the aggregation problem at the inward tip 153, frequently or daily washing the outer cup 15 is proposed. However, such a resolution usually makes busy the maintenance personnel, and reduces the application rate of the coating facility.